Metal is processed in a number of ways. For some metals the preferred form of production is in the form of ingots, which are then transported to metal working shops, for example rolling mills, for further processing and fabrication. Aluminum is one type of metal which is typically cast into ingots. Ingots may be made in various sizes, depending upon the size of the smelter and other factors. One common size for ingots is a large size which is commonly referred to as “sow”.
Casting aluminum ingots has certain requirements. For example, it is preferred if the casting can continue without stopping. This avoids having molten metal solidify where it is not desired, such as in a furnace or in a delivery launder or the like. However, continuous production requires continuous removal of molten metal, which in turn requires continuous casting. Continuous casting machines typically take the form of a circle, to permit continuous filling, removal and refilling of ingot forming moulds. In one common type of casting machine, a plurality of moulds are supporting in a casting ring, which in turn is supported from a central axle having radial arms supporting the casting ring.
As the ring indexes forward the moulds are poured to form ingots and then the ingots are slowly cooled. After cooling, the ingots are removed from the moulds and then the moulds are presented for refilling. Commonly, the carousel ring is driven from its center axle.
More recently, the ingots have been removed from the moulds by means of a vacuum system or apparatus. The apparatus typically includes a vacuum source, and an overhead vertically translatable vacuum head having a vacuum seal for engaging the ingots. To remove the ingots from the moulds, the vacuum seal is placed on the ingot, and the vacuum is initiated. The vacuum causes the vacuum seal to compress against the surface of the ingot. The ingot is then lifted out of the mould by the vertically translatable vacuum head.
There are a number of problems with the prior art systems as described above. First, the use of a central axle with arms supporting the ring requires very strong arms to support the cantilevered load of filled moulds. This requires a significant amount of structural support, which also adds to the overall weight of the carousel. The heavier the carousel is, the harder it is to make it rotate smoothly and the more powerful a drive is required. Stopping and starting the ring as each mould is indexed to the next station becomes more difficult the larger the ring is.
Further, having ring supporting arms that extend like spokes through and rotate through the inside of the ring renders the space inside the ring largely unusable. This in turn has a number of drawbacks. For example, the ring cannot be placed in a location where building columns would be positioned inside the ring, because such columns would interfere with the rotation of the arms. Also, the components of the ring are not accessible from inside the ring for maintenance and operational purposes, which reduces the flexibility of the machine. Furthermore, it is often useful to be able to position some system components, such as water piping for the ingot cooling means, inside the ring. However, the positioning of components inside the ring is made awkward and impractical by reason of the movement of the arms.
As well, even a very carefully moulded ingot has small sharp surface features which are an inevitable part of the moulding process. When the vacuum seal contacts the surface of the ingot, and the vacuum is engaged, the seal is sucked inward slightly, thus rubbing against the ingot surface, including the sharp surface features. To form the seal requires a flexible, rubber-like material. Even the best materials tend to get softer at higher temperatures, such as those associated with the recently poured ingots. It has been found that this combination of heat and abrasion quickly causes a loss of integrity of the seal leading to a failure of the lifting system. The system further requires a shutdown to permit the seal to be unfastened and replaced. This is typically made difficult, because in an effort to reduce wear on the seal, the seal is held in place by multiple fasteners which are difficult to remove, thus increasing down time and costs.
Therefore, what is desired is a metal ingot casting machine which overcomes the foregoing disadvantages. More specifically, it is highly desirable to be able to position the casting ring at any convenient location, without requiring the fully clear circular footprint of the prior art machines. As well, it would be preferred if the casting system could be provided with a ring which was lightweight and thus easy to motivate even when filled with metal ingots.